Change Video Speed
Processing entirely on your device — large files may take a moment.
Pick a rate and the video timestamps are rescaled while the audio passes through a tempo filter — speech and music speed up (or slow down) together with the picture, so nothing drifts out of sync.
The 0.5×-2× range matches what the audio filter can do in one pass — that is also the sweet spot where speech stays intelligible. Output keeps your input container.
How to change video speed
- 1
Select your files
Drag & drop your MP4 files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to MP4". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted MP4 file individually, or grab everything at once as a ZIP archive.
About the MP4 format
MP4 (MPEG-4 Part 14) is the universal delivery container of digital video. It wraps H.264, HEVC or AV1 video with AAC audio, and its structure — separate metadata (moov) and media atoms — is what makes streaming, seeking and fast-start playback possible. Phones, cameras, TVs, browsers and every social platform assume MP4 first.
Quality is entirely a function of the codec and bitrate chosen at encode time, so an MP4 can be a 10 Mbps HEVC master or a postage stamp. That flexibility plus total playback coverage is why nothing has displaced it in twenty years — conversion between formats almost always ends in MP4.
+Strengths
- ✓Plays on every device and platform in existence
- ✓Streaming-ready structure (fast start, seeking)
- ✓Choice of modern codecs: H.264, HEVC, AV1
!Limitations
- −Quality depends entirely on encode settings
- −HEVC variants hit licensing gaps on some platforms
Frequently asked questions
Does the pitch of the audio change?
Yes — atempo resamples the audio, so faster playback sounds higher-pitched (like a tape). Pitch-preserving speed change needs a phase vocoder, which the browser core does not ship.
Why not 3× or 0.25×?
The audio tempo filter is hard-limited to 0.5-2.0 per pass. Chain the tool twice for 4× (2× then 2× again).
Will the file size change?
Faster speeds shrink the file (fewer frames); slower speeds grow it. Quality per frame is preserved at CRF 23.